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Sci Signal. 2015 Dec 22;8(408):ra131. doi: 10.1126/scisignal.aab1901.

A calcium-accumulating region, CAR, in the channel Orai1 enhances Ca(2+) permeation and SOCE-induced gene transcription.

Author information

1
Institute of Biophysics, JKU Life Science Center, Johannes Kepler University Linz, Gruberstrasse 40, 4020 Linz, Austria.
2
Center for Nanobiology and Structural Biology, Institute of Microbiology, Academy of Sciences of the Czech Republic, Zamek 136, CZ-373 33, Nove Hrady, Czech Republic.
3
Faculty of Sciences, University of South Bohemia, Zamek 136, CZ-373 33, Nove Hrady, Czech Republic.
4
Institute for Experimental and Clinical Cell Therapy, Paracelsus Medical University, A-5020 Salzburg, Austria.
5
Institute for Biophysics of Medical University Graz, A-8010, Graz, Austria.
6
Department of Biophysics, School of Medicine, University of Saarland, D-66421 Homburg, Germany.
#
Contributed equally

Abstract

The Ca(2+) release-activated Ca(2+) channel mediates Ca(2+) influx in a plethora of cell types, thereby controlling diverse cellular functions. The channel complex is composed of stromal interaction molecule 1 (STIM1), an endoplasmic reticulum Ca(2+)-sensing protein, and Orai1, a plasma membrane Ca(2+) channel. Channels composed of STIM1 and Orai1 mediate Ca(2+) influx even at low extracellular Ca(2+) concentrations. We investigated whether the activity of Orai1 adapted to different environmental Ca(2+) concentrations. We used homology modeling and molecular dynamics simulations to predict the presence of an extracellular Ca(2+)-accumulating region (CAR) at the pore entrance of Orai1. Furthermore, simulations of Orai1 proteins with mutations in CAR, along with live-cell experiments, or simulations and electrophysiological recordings of the channel with transient, electrostatic loop3 interacting with loop1 (the site of CAR) determined that CAR enhanced Ca(2+) permeation most efficiently at low external Ca(2+) concentrations. Consistent with these results, cells expressing Orai1 CAR mutants exhibited impaired gene expression stimulated by the Ca(2+)-activated transcription factor nuclear factor of activated T cells (NFAT). We propose that the Orai1 channel architecture with a close proximity of CAR to the selectivity filter, which enables Ca(2+)-selective ion permeation, enhances the local extracellular Ca(2+) concentration to maintain Ca(2+)-dependent gene regulation even in environments with relatively low Ca(2+)concentrations.

PMID:
26696631
PMCID:
PMC5117258
DOI:
10.1126/scisignal.aab1901
[Indexed for MEDLINE]
Free PMC Article

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